The United Nation's Emergency relief chief says time is running out for survivors of the massive earthquake that demolished towns and villages in Pakistan. Frustration is also growing among relief workers who are having difficulty reaching some of the victims.

Demolished towns and villages litter the Himalayan region of Kashmir

A 5.6 magnitude aftershock rattled nerves and hampered relief efforts in remote villages, hit hard by Saturday's earthquake. The aftershock was centered 135 kilometers north of Islamabad, near the epicenter of Saturday's 7.6 magnitude quake that demolished towns and villages in the Himalayan regions of Kashmir.

Some villages are still waiting for assistance nearly one week after the earthquake.

Jan Egeland, the head of the UN's Emergency Relief team says time is running out.  He urged aid agencies to speed up relief efforts after the UN was accused of responding too slowly to the crisis.

Jan Egeland, UN Emergency Relief

"With no roads in the beginning, with very little international presence, and I think it's going as it could the first week, but I fear we are losing the race against the clock in these small villages around these centers."

Some roads leading to the devastated city of Muzaffarabad, the capital of Pakistan controlled Kashmir, were blocked due to landslides.

The World Food Programme (WFP) says convoys carrying 3 metric tonnes of food, enough to feed 2,000 families did not reach their destination.

Instead, WFP coordinator Keith Ursel says the food was distributed en route.

Keith Ursel, WFP coordinator

"Well. It's understandable that there are still aftershocks and still these roads being knocked out by rock slides, but it's extremely frustrating when you have truckloads of food and you can't reach the people just down the road."

Helicopters are proving vital in delivering much-needed aid. UN, NATO and U.S. Army helicopters have been deployed to speed up relief work but emergency workers say demand far exceeds the limited number of available helicopters. 

Mia Turner, WFP spokesperson

WFP spokesperson, Mia Turner says the choppers were used to distribute high-energy biscuits to survivors. "We're bringing in helicopters so that we can distribute to some of the 900 villages in this region -- only 30 percent of them are accessible.  It seems that the needs are very high and we're trying to reach all of them."

Search and rescue crews say time is also running out for survivors who may still be trapped inside collapsed buildings and rubble.

The death toll from the earthquake is believed to be more than 35,000, with tens of thousands more injured.  The UN estimates more than 2 million people are homeless and warned of possible outbreaks of measles and other diseases.

About 30 countries have sent equipment, doctors, paramedics, volunteers and disaster relief teams to help the earthquake victims.